Method of adjusting a helicopter blade trailing edge tab



Aug. 28, 1956 T. E. ZEERIP 2,760,588

METHOD DE ADJUSTING A HELICOPTER BLADE TRAIDING EDGE TAB Filed Feb. 28.1950 /f a 4 1% 5 -.1| j@ 19 l ...L y/////// f" P I 20A 17 l5 L@ i'W7/ll., g Il j 1 t 17 45g". L---rll r--ll--- I '.15 i A im l l il@ l@ YINVENTOR.

Tmfms Zee/a METHOD F ADJUS'HNG A VHELICOPTER BLADE TRAUJWG EDGE TABThomas E. Zeerip, Ridgefield, Conn., assignor to Doman Helicopters,Inc., Danbury, Conn., a corporation of Delaware Application February 28,1950, Serial No. 146,7 03

2 Claims. (Cl. 170'160.24)

The invention relates to a helicopter rotor head blade having anadjustable tab at the trailing edge thereof for varying or changing theaerodynamic contour of the blade. Blades of a helicopter are providedwith an adjustable or variable trailing edge in order to adjust the sameand secure aerodynamic tracking of the blades.

It is an object of the invention -to construct a blade having anadjustable tab, `the adjustment of which is secured by heating the tabuntil it becomes soft or plastic and easily bendable without stressingthe material beyond its elastic limit in order to secure a fixedadjustment of the tab.

Another object of the invention is the utilization of a trailing edgetab for a helicopter blade which is made of a thermoplastic materialwhich upon heating at a relatively low temperature becomes plastic foreasy bending or adjustment of the direction or plane of the tab.

Another object is to provide a tool for making the adjustment to thetrailing edge tab.

Other objects of the invention will be more apparent from the followingdescription when taken in connection with the accompanying drawings,illustrating a preferred embodiment of the invention, in which:

Figure l is a plan view of a helicopter blade;

Figure 2 is a cross section of the trailing edge of the blade on anenlarged scale;

Figure 3 is an end view of a tool for heating the tab to render the sameplastic and bendable;

Figure 4 is a plan view of the tool of Figure 3;

Figure 5 is an end view of another form of heating tool; and

Figure 6 is a plan view of the tool of Figure 5.

Helicopter blades have been provided with a metallic tab or tabsembedded or secured in some fashion to the trailing edge of the bladebending of which was used to secure aerodynamic trailing or tracking ofthe blades. These metal tabs are manually bent by stressing the metalbeyond its elastic limit so that the tab remains in adjusted or bentposition. Before a blade is aerodynamically adjusted for tracking onepoint in the tab may be bent rst in one direction and then as adjustmentat other points in the blade change the tracking may require bendingthis point again either to its original straight position or so that itbends in a reverse direction. This may occur several times at somepoints before the blade is aerodynamically adjusted or matched. As aconsequence the tab may be stressed too greatly and provide a fractureor at least a fatigue point where fracture will occur under the constantbending to which a blade is subjected in normal flight. In addition ametal tab is ditiicult to bend smoothly, is easily damaged in handlingeither separately or on the ship and is diiicult to obtain securefastening upon the trailing edge of the blade.

The invention herein utilizes an adjustable tab in the trailing edge ofthe helicopter blade which is thermoplastic at relatively lowtemperatures. The blade includes a spar 10 to which an aerodynamic body11 is secured of rates Patent O Patented Aug. `2.8., 19516 ice anydesired shape and construction. ,A tab 12 is vsecured to the trailingedge of the :blade or .bod-y in any suitable fashion, that particularlyillustrated being embedded between taper blocks 13 in the -trailing edgeVof the blade structure and secured thereto by known Aadhesives used inthe manufacture of 'the blade. Nails 1or Vscrews may also be used ifdesired. For a new 'blade .it is .embedded in the trailing edge at thesame time that the blade is glued together. The projecting .portion ofthe `tab is adjustable for aerodynamic vtracking of fthe blades and insome places along the vlength of the :tab :it may be bent downwardly andat other places it may be bent upwardly. The ltab extends preferably4along the whole length of the trailing edge of `the blade although `itmay extend along a lesser portion thereof. Preferably too, it is acontinuous strip. If a relatively thick .tab :is :used its trailing edgemay be vreduced to a ,narrow edge.

Synthetic resins or so called plastics provide thermoplastic materialswhich can 'be made soft and pliable or bendable by `heating them .to arelatively low temperature. That portion of the tab which projectsbeyond zthe blade body 1l or some portion thereof is heated vto `softenthe trailing edge -of the tab whereupon it `can then be bent when in aplastic `condition `to the desired `angle or position either upwardly ordownwardly. Since the material 1has been heated ,to a-plastic conditionthere .is no stressing for the material beyond its elastic limit inorder to x the adjustment to A,the ,desired angle or .position as withmetal tabs. Such adjustment therefore can be made indefinitely or atleast a great many times at any point without introducing any fixedstresses or causing internal fatigue of the material. There are manythermoplastic materials known to the synthetic plastic or resin art of`which nylon, is the preferred material for the trailing edge tab. Othersuitable organic thermoplastic materials are plasticized celluloseacetate, plasticized polyvinyl chloride, halogenated rubber, celluloseacetate-.butyrate, thermoplastic synthetic resins such as copolymer ofvinyl chloride and vinyl acetate, e. g. Vinylite polymerized esters ofacrylic acid, polystyrene, vinylidine chloride and the like. Thesematerials Abecome plastic or bendable upon heating to its respectivetemperature at which it becomes plastic which is under 400 degreescentigrade.

In order to adjust the thermoplastic trailing edge tab, the projectingportion or some portion thereof is heated to the temperature at which itbecomes soft and pliable whereupon it is bent to the desired positionwhereupon the heat is removed and the tab remains in the adjustedposition. Any means may be utilized to heat the tab to the propertemperature so that it may be bent. A convenient tool for this purposeis illustrated in Figures 3 through 6 which includes an electric heater16 of U-shaped form with a handle 17 extending therefrom. An electricheating pad 18 is provided in each leg of the U and may have athermostat 19 adjusted to give a predetermined heat depending upon thetemperature at which the thermoplastic material becomes soft enough foreasy bending and at which temperature, when the tool is removed, the tabremains in adjusted position. The tab 12 is inserted in the slot 20formed by the U-shaped tool and the tab is retained therein until it issoft, whereupon the tab is bent and the tool removed. In this manner thetab is adjusted at any desired point in its length without stressing theparticles of the material beyond their elastic limit in order to havethe tab remain in adjusted position.

Another form of tool is illustrated in Figures 5 and 6 in which theheating pad is in the handle but its operation is like that of Figures 3and 4. Like parts are given the same numerals and hence this tool neednot be described.

The thermoplastic trim tab has several advantages in addition to thosereferred to hereinbefore including more simplified means or method ofinstallation and it is easier to adjust. Also the tab is unaffected bycorrosion and weather.

The invention also embodies a method of adjusting a trailing edge tabfor a helicopter rotor head blade by heating the tab to a temperaturewhich renders it plastic and pliable or bendable Without stressing thesame beyond its elastic limit and to such a temperature depending uponthe material used that upon removing the heat it remains in its adjustedor bent position. The adjacent portions of the tab which are not heatedtend to support the heated portion so that it will remain in adjustedposition. rlhe length of the heated portion may be selected as desiredby the length of the heating device or tool.

Although the tab or tab means is preferably a continuous strip, it maycomprise separate sections of desired length at least in the portionthereof which extends or projects beyond the body of the Wing.

This invention is presented to ll a need for improvements in ahelicopter blade with trailing edge tab. It is understood that variousmodifications in structure, as well as changes in mode of operation,assembly, and manner of use, may and often do occur to those skilled inthe art, especially after benefiting from the teachings of an invention.Hence, it will be understood that this disclosure is illustrative ofpreferred means of embodying the invention in useful form by explainingthe construction, operation and advantages thereof.

What is claimed is:

l. A method of adjusting a trailing edge tab means of a helicopter rotorhead yblade which projects from the trailing edge of the blade body andis of organic thermoplastic material comprising heating at least someportion of the thermoplastic tab means which projects beyond the bladebody and which is to be bent to the temperature at which it `becomesplastic, bending this portion of the tab means when plastic, andremoving the heat theretrom whereupon the bent portion remains in bentposition.

2. A method of adjusting a trailing edge tab as in claim l `by heatingand bending other projecting portions of the thermoplastic tab meanswhich is to be bent.

References Cited inthe le of this patent UNITED STATES PATENTS 1,541,375Neuwirth et al. lune 9, 1925 1,609,110 Brown Nov. 30, 1929 1,754,993Fenton Apr, 15, 1930 1,843,886 Semmes Feb. 2, 1932 1,990,291 Larsen Feb.5, 1935 2,323,165 Thomas lune 29, 1943 2,335,296 Miller Nov. 30, 19432,417,586 Crosley Mar. 18, 1947 2,470,854 Kovac May 24, 1949 2,473,134Bonnet lune 14, 1949 2,514,092 Reese July 4, 1950 2,659,444 Stanley Nov.17, 1953

